1. Field of the Invention
The present invention relates to a cellulose hydrate-based flat or tubular film, its use as a food casing, preferably as a synthetic sausage casing, and a process for the production of the film and casing.
2. Description of Related Art
Cellulose hydrate-based flat, i.e., weblike, sheetlike or tubular films have long been known and are conventionally produced by the viscose process. In the viscose process an alkaline solution of cellulose xanthogenate, generally termed viscose solution, is extruded through a ring die or slot die and coagulated with acidic liquid as cellulose hydrate gel and regenerated to form cellulose hydrate. By means of the viscose composition and incorporation of additives, the properties of the tubular or flat body of the regenerated cellulose can be varied. The unreinforced cellulose hydrate films are also termed cellulose films and are known under the trademark Cellophane.RTM.. The films are also used as synthetic sausage casing, generally as so-called "small" casings.
In the production of fiber-reinforced bodies, a tubular or weblike fibrous material is coated on one or both surfaces with viscose solution and impregnated and then treated in an appropriate manner with coagulation and regeneration liquid. These fiber-reinforced casings are principally used for the production of naturally ripened and mold-ripened long-keeping sausage. It is also known to bend weblike cellulose films after their production to form a tube and to join the overlapping edges together, with formation of a longitudinal seam, or to produce the tubular casing seamlessly by extrusion of the viscose through a ring die.
Synthetic sausage casings based on cellulose perform important functions in the production, ripening and storage of the sausage product. They must be pliable and sufficiently extensible in order to be able to fill them, without any problems, with sausage meat to the desired caliber even after relatively long storage periods.
It is known to improve these properties by addition of secondary plasticizers such as glycerol. Since these plasticizers are not chemically bound to the cellulose hydrate but are only bound by intermolecular forces, they are dissolved out when the casing is moistened or when the sausage is simmered or boiled. The consequence is a particularly high brittleness of the plasticizer-free, dried cellulose casing after processing. This phenomenon is due to a crystallization proceeding in the cellulose material, the formation of hydrogen bonds between the individual cellulose molecules in the cellulose structure, and thus the closer proximity and spatial fixation of the molecules. As a result of this structural change, the casing becomes particularly impact-sensitive and frequently tears over the entire length on the first incision. All known cellulose hydrate casings, because of the described tendency to embrittling, are in need of improvement with respect to their pliability and extensibility.
In addition, cellulose hydrate casings must have a water permeation as low as possible. The permeation is decisive for the ripening behavior and mold growth in naturally ripened and mold-ripened long-keeping sausage. The uniform ripening of these sausage types demands a very slow release of water from the sausage mass during the first days. Therefore, when conventional fiber-reinforced cellulose casings are used, a very high and constant relative air humidity of the surroundings must prevail, for which reason the ripening of raw sausage has previously been carried out in ripening chambers in which the relative air humidity is controlled within narrow ranges.
An insufficient or varying moisture content of the ambient air leads to so-called dry rims on the outer periphery of the sausage. This particularly occurs when the casing material has an excessive permeation and the sausage mass, as a result, dries too quickly at the outer surface in the first days of ripening. The dried outer periphery of the sausage, the so-called dry edge, prevents the further exit of moisture from the interior of the sausage, so that it is still moist after the conventional ripening time. Moreover, the sausage casing no longer adheres sufficiently firmly to the dry edge, so that undesirable gaps develop between the sausage mass and the casing, and folds develop in the casing.
Furthermore, the mechanical strength and toughness of the cellulose hydrate casings are of particular importance. When the casings are being filled, in particular at high filling rates, there must be no breakdowns due to burst casings. These disadvantages occur, for example, in the case of the collagen fiber casings. Although collagen fiber casings are outstanding with respect to their permeation, they have completely inadequate mechanical strength. Similarly, alginate-modified casings which are not fiber-reinforced are not usable, because of their deficient mechanical strength, although the addition of alginate has very advantageous effects in the case of fiber-reinforced casings.
In addition, sausage manufacturers expect that cellulose hydrate casings show a consistency of caliber, i.e., that sausages which have been produced from the same casing material all have the same caliber within narrow ranges. Caliber is defined as the inside diameter of the casing. In this regard, casings are in need of improvement, especially casings which are not fiber reinforced.
A further quality characteristic of cellulose hydrate casings is their moisture balance. On the one hand, the material should have a high water imbibition, i.e., should absorb amounts of water as large as possible. On the other hand, at the same time, delayed water release is desired. The capacity for water absorption and release is not equivalent to, or correlated with, the permeation. The permeation is a measure of the water permeability of the casing, while the moisture balance characterizes the water absorption capacity and water binding capacity of the casing. A good moisture balance ensures a problem-free drying process, in which no brittleness or overdrying of the casing occurs.